1. Field of the Invention
The present invention relates to an apparatus for measuring the permeability of a circulating band, in particular of a dewatering band in a papermaking machine, having a nozzle from which a measuring fluid flows onto the band.
2. Description of the Related Art
Permeability measurements on circulating bands generally have to be carried out with a high pressure of the measuring fluid in order that the stream of measuring fluid can penetrate the band. It is therefore necessary to press the nozzle correspondingly firmly against the band, since the volume flow of the measuring fluid produces a correspondingly high reaction force on the nozzle, and thus forces the nozzle away from the band. In particular, when pressure fluctuations occur in the volume flow of the measuring fluid, there is the risk that the nozzle is lifted off the band by the reaction force acting on it, which can result in an erroneous permeability measurement.
What is needed in the art is an improved apparatus where the nozzle is prevented from lifting off the band in the event of pressure peaks as a result of pressure fluctuations in the measuring fluid.